1. Field of the Invention
This invention relates to a supporting system for supporting an outboard propulsion unit to a boat, and more particularly to such an outboard propulsion unit supporting system for allowing the propulsion unit to be displaced vertically and tilted relative to the boat.
2. Description of the Prior Art
Hitherto smaller ships and boats are provided at their transom with an outboard propulsion unit thereby to generate propulsion force. Now it has been proposed and put into practical use to provide a device which causes the propulsion unit to be displaced upwardly and downwardly and tilted relative to the boat, in which a propeller is installed at the lower end of the boat. With such a device, for example during cruising on the shoal, the propulsion unit with the propeller is raised upwardly thereby preventing the propeller from breakage due to interference with rock and reef. Additionally, the propulsion unit with the propeller is controllably displaced upwardly or downwardly to obtain the maximum thrust during cruising. Such a mechanism for displacing the location of the propeller upwardly and downwardly is disclosed, for example, in Japanese Patent Provisional Publication No. 61-12497, in which a boat side member and a propulsion unit side member are connected with each other by upper and lower links to constitute a generally rectangular link mechanism. The angle of the upper and lower links relative to a boat transom is changed by a lift cylinder, thereby displacing the propulsion unit upwardly or downwardly relative to the boat.
However, with the arrangement of the Japanese Patent Provisional Publication, the distance between the boat transom and the outboard propulsion unit changes with upward and downward displacement of the propulsion unit since the propulsion unit is supported to the boat transom through the rectangular link mechanism. By the way, there is a fear of generating water spray to be sprinkled over the boat owing to impingement of water flow from the boat rear section against the outboard propulsion unit during cruising, because the outboard propulsion unit is supported rearwardly separate from the boat transom. Hitherto in order to prevent this water spray generation, various measures have been taken in which the front side of the propulsion unit is formed into the particular shape to suppress generation of water spray; however, such measures are usually made to be the most effective at a certain fixed distance between the boat transom and the propulsion unit. As a result, the above-mentioned change in the distance between the boat transom and the propulsion unit causes adjustment to get out of order thereby allowing sprashed water to be sprinkled over the boat. Furthermore, since the propulsion unit has a larger weight, change of the position of the propulsion unit relative to the boat causes the center of the gravity to be displaced, thereby resulting in trimming change.